Currently, most computer mice have optical/laser based sensors. Older or more conventional units feature mechanical type balls. All of these interpret a user's movement and send associated signals to a host device. Mice also comprise one or more buttons and potentially other input controls such as scroll wheels/tilt wheels and programmable buttons to accept user input. The mouse may be directly connected to the host computer via a wire or wirelessly through radio, I/R or some other method. Typically, the most expensive components in a mouse are the microcontroller, the optical/laser sensor and the wireless transmission component (if any).
A user typically must select from several pre-determined shapes provided by the mouse manufacturer.
This necessitates most manufacturers making several mice to suit the requirements of various users, even though each mouse with different shapes may have common internal components (i.e., the microcontroller, sensor and wireless component).
In order to provide users with different ergonomic designs and functionality while sharing the common internal components, existing approaches include:    1. “Mini mouse” —A very small mouse, which accepts larger cases on top. The limitation of this is that there is not much flexibility, the additional cases merely ride piggy back and the larger mouse buttons simply actuate the existing “Mini mouse” button. This tends to lead to mechanical inaccuracy and requires parts to be manufactured to extremely high tolerances, which may not be cost effective.    2. “Multi-case mouse” —This design has either multiple top covers meant to fit onto one existing bottom cover, or the internal PCB is designed to be unscrewed from one case and screwed into another case. The disadvantage here is that in a multiple button and scroll wheel positions of the bottom cover. There is also some danger since the internal circuitry is not shielded from the lay user who may accidentally damage it when changing cases.